The role of the classical and alternative pathway of complement activation in the rheumatic diseases is being studied by the use of metabolic studies on patients with rheumatic diseases. The role of the various autoantibodies in activation of the complement systems is also being explored. The pathophysiologic significance of deposition of immunoglobulins and complement in skin and kidney in patients with systemic lupus erythematosus and other rheumatic diseases is being explored in relation to metabolic studies.